1. FIELD OF THE INVENTION
This invention relates to the field of mechanisms for angularly deflecting energy beams, specifically in a pattern generation system
2. BACKGROUND ART
In the photolithographic fabrication of integrated circuits, films sensitive to radiant or particle energy are exposed in predetermined patterns to define circuit features. In some cases, the energy is passed through masks which contain the patterns, thereby selectively exposing a photoresist film on a semiconductor body. In other instances, the film is on a mask substrate and the film is exposed as a step in the making of the mask. Other times, the direction of the radiant energy itself is controlled to define patterns in the film. This can be done as part of making the mask or to directly "write" onto the photoresist film covering a semiconductor wafer. Several sources of radiant energy have been used, including ultraviolet light, visible light, coherent light, x-rays and electron beam (E-beam). Current technology utilizes lasers to fabricate masks by directing a laser beam and/or moving a work piece relative to the laser beam. One method for generating these masks utilizing lasers is found in U.S. patent application No. 758,344 filed July 24, 1985 entitled "Laser Pattern Generation Apparatus" and assigned to the assignee of the present invention, now abandoned.
In this system, a laser is used to write a pattern on a workpiece. The workpiece moves beneath the laser, which is held stationary. However, the accuracy required to write complex circuit patterns requires that the laser be adjusted relative to movement of the stage on which the workpiece rests.
One method of providing such adjustment is by use of steering mirror. The laser is reflected off the steering mirror, through an optical path including lenses and beam splitters, and ultimately onto the workpiece. By altering the angle at which the laser strikes the steering mirror, the point at which the beam strikes the workpiece can be controlled. This allows correction of relative beam/workpiece movement.
In the prior art, steering mirrors are mounted on a galvanometer. The galvanometer has the disadvantage of low torque resulting in slow frequency response. Additionally, the minimum angle of movement which can be detected when using the galvanometer limits the accuracy of such prior art systems.
Therefore, it is an object of the present invention to provide a steering mirror which can be operated with a maximum frequency response.
It is yet another object of the present invention to provide a steering mirror of minimum inertia. (Minimize forces transmitted to supporting structure.)
It is yet another object of the present invention to provide minimum energy (minimize heat dissipation to prevent thermal distortion of support and mechanism.)
It is another object of the present invention to provide a steering mirror which can be adjusted in small angles, providing a more accurate steering mirror.
It is yet another object of the present invention to provide a steering mirror with a position detection mechanism for more accurate positioning of a reflected beam.